The
testa or seed coat of some
seeds is hard and quite
impermeable to
water and gases (e.g. the
seeds of
Sclerocactus, Pediocactus and
Toumeya ); This
seeds will not germinate
unless their seed coats has been altered physically. The seed
coat is not really required for germination. In fact, many seeds
do have a hard seed coat which is a physical
barrier (external
dormancy) that
prevents germination. Any
process of breaking, softening, drilling, scratching, or
mechanically altering the seed coat to make it
permeable to water and
gases is known as scarification. Through this alteration
of the testa the seed can
imbibe water.
In nature, this occurs as the seed exposed to freezing
temperatures or microbial activities that modify the seed coat
during the winter. Scarification can also occur as seeds pass
through the digestive tract of various birds and animals.
Methods of scarification commonly used are mechanical, hot
water, and acid.

MECHANICAL SCARIFICATION

Involves breaking or weakening the seed coat and
can be carried out using sandpaper or a file to abrade the seed
coat, or using a knife to nick the coat, or using an hammer to
crack the the coat for allowing water to enter. Make attention
to not crush the seed as to damage the
embryo. Once
scarified, seeds will not store well and should be planted as
soon as possible after treatment or placed under cold/moist
stratification
if required. This treatment works well for larger seeds. Smaller
seeds may be rubbed between sheets of fine grit sandpaper. If
the seeds are too small to see the progress, a different method
such as soaking should be used.

HOT WATER SCARIFICATION

Some seed coat can be softened in warm or hot
water ( 75-95° C NOT BOILING! ) the seeds are left to
soak in the water as it
cools for 12 to 24 hours before planting. Use 10-20 times the
volume of hot water versus seed. Seeds with a
waxy coating should be washed
several times in very hot water to remove the
wax before the final
soaking.

ACID SCARIFICATION

The seeds are put in a glass container (Do not use any other type)
and covered with concentrated sulphuric acid at about twice the
volume of seed. The seeds are gently stirred and allowed to soak
from 10 minutes to several hours depending on the hardness of the
seed coat. When the seed coat becomes thin, the seeds can be
removed, washed and planted. This method involves the use of
concentrated Sulphuric acid that is a very hazardous chemicals that
can, be very dangerous for an inexperienced individual and requires
to observe meticulous SAFETY measures that should not be overlooked!
It is very important to remember to NEVER pour water into acid!
ALWAYS pour the acid into the water!!!

Various reference books provide appropriate concentrations and
durations of treatment.

Some species of climbing
plants develop holdfast roots which help to support the vines on
trees, walls, and rocks. By forcing their way into minute pores and
crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron
radicans), Boston ivy (Parthenocissus
tricuspidata), and trumpet creeper (Campsis
radicans), develop holdfast roots which help to
support the vines on trees, walls, and rocks. By forcing their
way into minute pores and crevices, they hold the plant firmly
in place. Usually the Holdfast roots die at the end of the first
season, but in some species they are perennial. In the tropics
some of the large climbing plants have hold-fast roots by which
they attach themselves, and long, cord-like roots that extend
downward through the air and may lengthen and branch for several
years until they strike the soil and become absorbent roots.